Monitoring device for positive pressure breathing apparatus

ABSTRACT

THE RESPIRATITON PRESSURE OF A PATIENT BEING TREATED WITH POSITIVE PRESSURE BREATHING APPARATUS IS USED FOR CLOSING AN ELECTRIC SWITCH DURING EACH INHALATION CYCLE. EVERY TIME THE SWITCH IS CLOSED AN ELECTRIC CHARGE IS DELIVERED TO A FIRST CONDENSER, WHICH IS DISCHARGED AT REGULAR INTERVALS, BUT A FIRST ELECTRIC SIGNAL INDICATOR FOR EXCESSIVE BREATHING RATE WILL BE ACTUATED BY THE CHARGE BUILT UP ON THE CONDENSER IF IT REACHES A PREDETERMINED VALUE BEFORE THE CONDENSER IS DISCHARGED. THERE ALSO IS A SECOND CONDENSER AND MEANS FOR CHARGING THE CONDENSER CONTINUOUSLY, AS WELL AS MEANS FOR DISCHARGING IF EVERY TIME THE SWITCH IS OPENED. A SECOND ELECTRIC SIGNAL INDICATOR FOR INADEQUATE BREATHING RATE WILL BE ACTUATED BY THE CHARGE BUILT UP ON THE SECONDENSER IF IT REACHES A PREDETERMINED VALUE BEFORE THE CONDENSER IS DISCHARGED.

MONITCRING DEVICE FOR POSITIVE PRESSURE BREATHING APPARATUS Filed Nov.14. 19e? A TTR/VEKS United States Patent O 3,566,387 MONITORING DEVICEFOR POSITIVE PRESSURE BREATHING APPARATUS Allen G. Schoener, Verona,Ellison L. Davison, Glenshaw, and Glenn H. Fertig, Cheswick, Pa.,assignors to Mine Safety Appliances Company, Pittsburgh, Pa., acorporation of Pennsylvania Filed Nov. 14, 1967, Ser, No. 682,895 Int.Cl. G08b 23/00 U5. Cl. 340-279 Claims ABSTRACT OF THE DISCLOSURE Therespiration pressure of a patient being treated with positive pressurebreathing apparatus is used for closing an electric switch during eachinhalation cycle. Every time the switch is closed an electric charge isdelivered to a rst condenser, which is discharged at regular intervals,but a first electric signal indicator for excessive breathing rate willbe actuated by the charge built up on the condenser if it reaches apredetermined value before the condenser is discharged. There also is asecond condenser and means for charging the condenser continuously, aswell as means for discharging it every time the switch is opened. Asecond electric signal indicator for inadequate breathing rate will beactuated by the charge built up on the second condenser if it reaches apredetermined value before that condenser is discharged.

It is among the objects of this invention to provide a device thatmonitors the respiratory pattern being delivered by intermittentpositive pressure breathing apparatus to a patient and signals anysignificant deviation from that pattern. More specically, the device isdesigned to signal if the patient respiration pressure fails to attain apreset minimum or exceeds a preset maximum, and also to signal if therespiration rate falls below a preset minimum or exceeds a presetmaximum.

The invention is illustrated in the accompanying drawing, in which thesingle figure is a circuit diagram for our monitoring device.

Referring to the drawing, a normally open electric switch 1 has onecontact connected by a conductor 2 with one terminal of a battery 3 andthe other contact connected through a resistor 4 and a conductor 5 withthe other terminal of the battery. The switch may be a magnetic switchthat is closed when a magnet 6 is moved close enough to it. 'The magnetmay be supported by a leaf spring 7 between the switch and a movablewall, preferably in the form of a flexible diaphragm 8, that forms onewall of a housing 9. 'The side of the housing is provided with an inlet10 that is connected by a tube 11 with the breathing hose 12 thatconnects any intermittent positive breathing apparatus 13 with a mask 14worn by a patient, whereby the inside of the housing is subjected to theair or oxygen pressure in the breathing hose. During the pressure orinhalation cycle of the breathing apparatus, the gas pressure in thehousing becomes great enough to cause the diaphragm to move the magnettoward the switch so that the switch will be closed. The pressure thatis required for this purpose may be determined by an adjustable cam 15that is used for pre-loading the magnet spring. Thus, the switch isclosed at a preset pressure periodically at the respiration rate of thepatient.

Each time the switch is actuated to a predetermined position, which isthe closed position in the circuit described, a ditferentiator circuit,consisting of resistors 4 and 17 in parallel and a capacitor 18 inseries with resistor 17, produces a negative pulse that causes atransistor 19 to become nonconductive for the duration of ACC the pulse.While the transistor is nonconductive, the voltage at its collectorrises at a rate determined by the time constant of a variable resistorZll and a condenser 22 which are connected by a diode 23. Those lastthree elements are connected in series across conductors 2 and 5. Due tothe unidirectional effect of the diode, the voltage just mentioned isstored on the condenser. If the charge is allowed to build up withoutinterruption, it will increase to the firing point of a unijunctiontransistor 25, whereupon a positive pulse is produced across a resistor26 connecting this transistor with conductor 2. This causes a siliconcontrol rectifier 27 to conduct. The rectifier connects to conductor 2 asignal indicator, such as a lamp 28, that also is connected through aresistor 29 and a normally closed reset switch 30 with conductor 5. Whenthe lamp is lit, electric current ilows through resistor 29, thuscreating a voltage drop that causes a transistor 32 to enter anonconductive state by `way of a capacitor 33 and a resistor 34 that areconnected in parallel with each other between conductor 5 and thetransistor. When transistor 32 becomes nonconductive, a relay 3'5 inseries with it is released, which opens the power circuit to thetransistor and closes a separate circuit containing a battery 36 and anaudible alarm, such as a buzzer 37. The buzzer and lamp will continue tofunction until a normally open reset switch 38 is closed momentarily.The two reset switches are mechanically connected so that closing switch38 opens reset switch 30 momentarily. Switch 38 connects the relay backin circuit and reverses it to open the buzzer circuit, and openingswitch 30 extinguishes the lamp and renders rectier 27 nonconductiveagain. It will also be seen that if there is a power failure in the maincircuit, relay 35 will be released and the buzzer will sound the alarm.

The system described thus far shows that a signal or alarm is actuatedwhenever suicient voltage is built up on condenser 22 to tireunijunction transistor 25. However, this build-up does not occur if therespiration rate of the patient does not exceed the desired rate forwhich the device is set. Prevention of voltage build-up is accomplishedby timing means that discharge the condenser at regular intervals shortenough to normally not leave enough time for the condenser to be chargedto the value necessary for firing the unijunction transistor. Forexample, timing means may be used that will discharge the condenserevery 30 seconds, in which case variable resistor 21 is set to requiremore than the expected number of closings of switch 1 in 30 seconds tocharge the condenser to the alarm point. Therefore, as long as thepatient does not breathe faster than intended, the switch will not closeenough times in 3() seconds to charge condenser 22 to the point where itwill re transistor 25. However, if the respiration rate increases sothat the switch is closed more frequently in the same selected period oftime, a signaling voltage will be built up on the condenser.

The timer may take the form of a unijunction transistor 41 inconjunction with a capacitorl 42 and a resistor 43. The last twoelements are connected across conductors 2 and 5. The three elementsgenerate a positive pulse which is distributed across a resistor 44 atregular intervals, such as every 30 seconds, for example. When thishappens a transistor 45 is made conductive momentarily and dischargescondenser 22, with which it is connected in parallel. Consequently,under normal conditions the condenser is discharged every 30 secondsbefore it can acquire a large enough charge to cause the lamp to lightand the buzzer to sound, but if the respiration rate rises above thedesired value, the alarm will be actuated.

Another feature of this invention is that the device will signal in casethe respiration rate of a patient falls below the minimum rate it isdesired to maintain. T0 accomplish this, a condenser 50 is connected inseries with a variable resistor 51 across conductors 2 and 5, so thatthe condenser is charged continuously at a rate controlled by variableresistor 51. If sufficient voltage is stored on this condenser, it willre a unijunction tran.- sistor 52, thereby producing a pulse across aresistor 53 which causes a silicon control rectier 54 to conduct andpermit a second signal lamp 55 to light. The rectifier connects one sideof the lamp `with conductor 2 and the other side is connected by aconductor 56 to a point between lamp 28 and resistor 29. When lamp 55 islit, a current ilow is created through resistor 29 and produces avoltage drop that causes transistor 32 to enter a nonconductive stateand thereby release relay 35 so that the buzzer will sound until resetswitch 38 is closed again and reset switch 30 is opened simultaneouslyas previously explained. l

To prevent lamp 55 from lighting while the minimu respiration rate issatisfactory, which means that there are not too few respirations perminute, condenser is discharged periodically 'before suicient voltage isstored on it to tire transistor 52. This discharging of the condenser isaccomplished by a transistor 60 in parallel with it. The transistornormally does not conduct, but every time the pressure switch 1 isactuated to a predetermined position, the open position as shown, apositive pulse is injected into the base of the transistor to make itconduct and discharge condenser 50. The time that it takes for asignaling voltage to build up on condenser 50 can be adjusted byvariable resistor 51. A time period is selected that is slightly greaterthan the period between successive openings of the switch while thebreathing rate is above the minimum desired, so that under normaloperating conditions condenser '50 will be discharged before it canstore a tiring voltage.

Due to a capacitor 61 connected between conductor 5 and the base of thetransistor, and a resistor 62 connected 'between the base of thetransistor and conductor 2, transistor 60 conducts only momentarily andimmediately becomes nonconductive again so that charging of condenser 50can begin again. Therefore, if the respiration pressure is notsuflicient to close the switch, enough voltage will build up oncondenser 50 to cause lamp 55 to light. A drop in the respirationpressure may be due to a leak in the air stream of the breathingapparatus, or to loosening or loss by the patient of the mouthpiece,face mask or tracheotomy adapter. Lighting of the lamp can mean thateither the respiration rate or the respiration pressure is too low.

By the addition of further transistors to the circuits in a knownmanner, transistor 19 could be made nonconductive every time switch 1 isopened instead of closed, and transistor could be made conductive everytime the switch is closed instead of opened.

A further feature is that this system can also be used for giving analarm in case the respiration pressure becomes too great. This mightoccur if the patient suers a severe airway obstruction or a mucousblock. To give such an alarm a second pressure operated switch 65 isprovided that likewise may be magnetic and closed by a magnet 66 mountedon the end of a leaf spring 67 that can 4be pre-loaded by a cam 68. Tomove the magnet t0- ward the switch, the side of housing 9 oppositeswitch 1 likewise is provided with a movable wall, such as a flexiblediaphragm 69, that will be moved outwardly to close switch 65 if thepressure in the housing rises above a predetermined maximum determinedby the setting of cam 68. Closing of switch 65 creates a positive pulse,which is delivered to the gate of a silicon control rectifier 71 by wayof a pair of resistors 72 and 73 and a capacitor 74. The pulse causesthe rectifier to conduct and that connects a third signal lamp 75 intothe circuit between wire 56 and conductor 2. When the lamp is lit,current `ilows through resistor 29 and creates a voltage drop to causetransistor 32 to become nonconductive. The result is that relay 35 isreleased and the alarm buzzer sounded. The lamp remains lit and thebuzzer continues to buzz until the reset switches are operated.

To prevent a sudden but transistory increase in pressure from closingswitch 65, a partition 77 is disposed inside housing 9 between inlet 10and diaphragm 69. This partition divides the inside of the housing intotwo chambers that are connected by an aperture 78 in the partition. Ifthe patient happens to cough and thereby suddenly increase the pressurein the larger chamber, this pressure will be prevented by the partitionfrom reaching the other chamber and closing switch 65. That is, beforethe momentary increased pressure in the large chamber can be transmittedthrough the small hole in the partition to the other chamber, thebreathing apparatuswill have switched to the exhalation cycle and thepressure in the housing will be reduced.

According to the provisions of the patent statutes, we have explainedthe principle of our invention and have illustrated and described whatwe now consider to represent its best embodiment. However, we desire tohave it understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically illustratedand described.

We claim:

1. A monitoring device for breating apparatus comprising an electricswitch movable between open and closed positions and normally in one ofsaid positions, means actuated by patient respiration pressure above apredetermined minimum for periodically moving the switch to the other ofsaid positions, a rst condenser, means for charging the condenser everytime the switch is actuated to said other position, means fordischarging the condenser at regular intervals, a rst electric signalindicator for excessive `breathing rate adapted to be actuated inresponse to the charge built up on the condenser if it reaches apredetermined value before the condenser is discharged, a secondcondenser, means for charging the second condenser continuously, meansfor discharging the second condenser every time said switch returns tosaid normal position, and a second electric signal indicator forinadequate breathing rate adapted to be actuated in response to thecharge built up on the second condenser if it reaches a predeterminedvalue before that condenser is discharged.

2. A monitoring device according to claim 1, in which said normalposition of the switch is its open position.

3. A monitoring device according to claim 1, in which said normalposition of the switch is its open position, and said second condenserdischarging means are effective only momentarily, whereby a charge willbe built up on the second condenser to said last-mentioned predeterminedvalue if said respiration pressure becomes insuicient to close saidswitch.

4. A monitoring device according to claim 1, in which said signalindicators are electric lamps, said device including an electric audiblealarm, an electric circuit for energizing the alarm, a normally openswitch in said circuit, and means causing that switch to close whenevereither of said lamps is lit.

5. A monitoring device according to claim 1, in which each of saiddischarging means includes a normally nonconductive transistor inparallel with one of said condensers, and means for rendering thetransistors conductive periodically.

References Cited UNITED STATES PATENTS 8/1964 Haber 128-4l9UX 8/1967Andreasen et al. 340-239

